Neoadjuvant chemoradiotherapy has played an important role in preserving organs and functions in patients with oral squamous cell carcinoma (SCC). To determine whether further operation after chemoradiotherapy is necessary, accurate evaluation of residual tumour cells after treatment is essential. We investigated the usefulness of regional fluorodeoxyglucose (FDG) uptake in combination with histochemical expression of AgNORs obtained from pretreatment biopsy specimens to assess residual tumours after intraarterial chemoradiotherapy. Standardized uptake value (SUV: pretreatment, pre-SUV; post-treatment, post-SUV) was calculated to determine the changes of FDG uptake in the tumour before and after chemoradiotherapy. Four out of 20 patients with oral SCCs showed residual tumour cells after treatment. Tumours with higher post-SUVs (> or =4.0) and higher AgNORs scores (> or =5.0) had significantly higher incidences of residual viable tumour cells after chemoradiotherapy (P=0.001). The results suggest that the combination of FDG-PET with AgNORs score is an excellent index for determining the optimal management of each patient following neoadjuvant chemoradiotherapy.